We have been installing heat pumps for 70 years.
By and large they have been marketed as "air conditioners".
Yes. Those are heat pumps. For reasons which boggle me, very few were sold with the 1 additional part that would allow them to switch from A/C to heat. But the operating principle is exactly the same.
So I for one would expect longevity of heat pumps to resemble air conditioners.
Obsolescence has largely been about efficiency
And also changes in operating gas. You know, we started with the "miracle product" called CFCs - which as it turned out, led to another miracle product called sunblock since it chewed a hole in the ozone layer. That was the R12 and R22 "Freon" refrigerant. And then in the 90s we shifted gears to R-134a refrigerant. That was better, but still had issues, so we have upgraded again to the latest variety of refrigerants.
This isn't a fashion thing; we were driven away from R22 and R12 because they did too much damage to the ozone layer, and R134a because it contributes heavily to global warming. That is solved now, so the newest refrigerant choices are about effective temperature range (the newest ones work in Chicago), efficiency and cost.
And that applies to new products, already-installed ones "run til they drop" - or in the case of the oldest units, run 'til you can't get refrigerant anymore.